As described in commonly owned U.S. Pat. No. 5,634,531 an automatic lubricant dispenser has a vessel adapted to hold a supply of a fluent lubricant and having one side formed with an outlet adapted to be connected to a machine to be lubricated and an opposite side, a piston in the vessel movable forward toward the one side to force the lubricant from the outlet, and an electric drive connected to the piston and electrically energizable to advance the piston forward. An electric power source is connected via an electrical circuit to the drive for periodically energizing the drive and thereby advancing the piston an increment and pumping a dose of the lubricant from the outlet.
German utility model 9,214,096 describes such a system where the motor has a rotary output shaft connected via gearing to a spindle threaded into the piston which is prevented from rotating. The motor is powered from batteries mounted in the dispenser housing. The housing is formed by a lower part that forms together with the piston a compartment filled with a fluent lubricant and an upper part containing the motor and batteries. The threaded spindle fixed to the transmission of the electric-motor drive unit is threaded into the piston which is impeded from rotating so that, when the spindle rotates, the piston is advanced.
When the supply of lubricant is exhausted, the motor is reversed to its starting position with the piston all the way up. Then the upper housing part and motor unit are separated from the lower housing part which is in turn disconnected from the feed line to the machine being lubricated. A new lower part filled with lubricant is installed, the upper housing part is fitted in place, and the system can be restarted.
The disadvantage of this system is that if the piston is not perfectly positioned when a new lower lubricant-filled housing part is installed there can be problems. If the piston is too low it will now allow the assembly to be put back together without extruding out some of the lubricant and making a mess. If it is too high, for the first couple of cycles the piston will move without actually contacting or pressurizing the lubricant mass so that no lubricant dosing will take place. In general it is difficult to provide such a system with a new lubricant supply.